A light-emitting diode (which hereinafter may also be referred to as “LED”) is generally formed by arranging an LED device on the bottom portion of a cup-shaped sealing member in a package, and sealing it with a sealing resin. Conventionally, as an LED sealing resin, a light-transmitting resin including an epoxy resin, a silicone resin, or the like is used.
It is believed that an LED sealing resin has better light extraction efficiency as it has less of a difference in the refractive index from an LED device according to Snell's Law. For this reason, as an LED sealing resin, those resins having higher refractive index are preferably used.
Examples of a sealing resin having a high refractive index include resins having an aromatic ring such as a phenyl group in the skeleton, such as an epoxy resin. However, an aromatic ring causes a problem in that coloration occurs by oxidation under UV excitation.
Furthermore, since a resin having a heavy atom such as sulfur has a high refractive index, there has been proposed that a resin having a high refractive index and containing sulfur is coated onto a light extraction surface of a light-emitting device (see, for example, Patent Document 1). However, a sulfur compound causes a problem in that coloration occurs on Ag plating or coloration occurs by a thermal decomposition.
Furthermore, it has been known that it is possible to improve the refractive index of a resin while maintaining its transparency by dispersing fine particles having high refractive indexes in a resin to make a resin composition. For example, Patent Document 2 describes a liquid curable resin composition which contains a multifunctional (meth)acrylic compound, a reaction product obtained by reacting a compound having a polymerizable unsaturated group and an alkoxysilane group in the molecule with the oxide particles of a metal, and a radiation polymerization initiator.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2000-49387
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2000-143924